Crease resistant finishing is used to improve the elasticity of many textile fabrics. The finished fabric can have remarkably increased wrinkle resistance and dimension stability, and such wrinkle resistance can persist even after the fabric is machine washed and tumble dried many times.
Amino-formaldehyde (N-methanol) resins have been widely used in crease resistant finishes. Although amino-formaldehyde resins are quite effective in improving crease resistance, they release formaldehyde vapor during their manufacture, while they are in storage, and also when in use by consumers. Formaldehyde vapor irritates human eyes and skin, and is a known carcinogen.
Partly because of the serious health problems associated with formaldehyde, much research is currently directed to developing formaldehyde-free fabric finishes. Most of the research relates to cotton fabrics. The major non-formaldehyde finishes reported for cotton crease-resistant finishing are polycarboxylic acids, for example, citrus acid and butanetetracarboxylic acid (BTCA).
Polycarboxylic acids are said to esterify and cross-link with cellulose fibers of the cotton at elevated temperatures and in the presence of catalysts. Catalysts described for cross-linking cellulose fibers include basic salts selected from the alkali metal dihydrogen phosphates and alkali metal salts of phosphorous, hypo-phosphorous, and polyphosphoric acids. Polycarboxylic acid cross-linking is said to be applicable to fibrous cellulosic materials such as cotton, flute, jute, hemp, and also for regenerated wood celluloses, such as rayon.
BTCA, a polycarboxylic acid, is said to produce an improvement in the wrinkle recovery and water-washing durability of cotton fabrics. BTCA reportedly exhibits a very low volatility, releases no formaldehyde, and is odorless after cross-linking with the cotton fabric. Additionally, BTCA is reported to have low activity as a skin irritant and low oral and dermal toxicity in animal tests.
Fibers obtained from animals, such as silk, differ substantially from vegetable fibers, such as cotton and hemp. The animal fibers contain keratin and are chemically distinguishable from the cellulose fibers obtained from vegetables. A process for modifying keratinous material has been described which includes treating keratinous fibers with a mixture containing polythiols obtained from carboxylic acids, nitrogen-containing condensation products of epoxides, fatty amines, and dicarboxylic acids and, optionally, stabilizers against the harmful action of light. The process reportedly renders the keratinous material resistant to shrinkage and imparts desirable, durable press characteristics to the material.
A process for improving properties of silk, such as abrasion resistance and light resistance has been reported which involves a cross-linking treatment of silk fiber with epoxy compounds. In the process, the silk fibers are said to be treated with an aqueous solution containing a water-soluble epoxy compound in a catalyst which may be selected from alkali metal or alkali earth metal salts of dicarboxylic acids, tricarboxylic acids, and amino carboxylic acids. The process may include a heat-treating step at temperatures of 50.degree. to 110.degree. C.
Silk textiles are universally popular for use in clothing. They are comfortable to wear and provide an elegant appearance. However, silk textiles generally wrinkle and deform permanently if washed in water. For this reason, silk fabric is said to have a low wet elasticity. Although silk can be dry cleaned, dry cleaning is expensive and is relatively ineffective at removing certain types of stains, for example, perspiration stains.
Chemical finishes are available which improve some of the commercially important properties of silk. For example, glyoxal resin finishes with ethylene urea are reported to produce a silk textile having good crease-recovery, particularly when used with a metal-acid catalyst. Also, urethane resins with or without formaldehyde are said to be suitable for producing machine-washable silk. Generally, the resins are applied from an aqueous bath on a stenter, dried, and cured at about 150.degree. C.
It has been reported that epoxides, siloxanes, aminoplasts and glyoxal can be dispersed in a sodium-hydroxide solution and applied to silk textiles to increase the washability of the textiles. Similarly, others have reportedly applied hydroxymethylmethacrylamine to improve crease-resistance and dimensional stability. Others are said to employ a combination of glycerol and ammonium chloride to increase wrinkle recovery.
A process for preventing damage to fibers of natural protein-containing fiber materials has been reported which employs water soluble polyamides. Polyamides are said to be produced by reacting aliphatic polyamines with a polycarboxylic acid. The natural protein-containing fibers can be wool, silk, vegetable, or synthetic fiber materials. The process is said to preserve wet tear-resistance of fibers that are immersed in an aqueous acidic medium, such as a dye solution.
However, the wide appeal of silk textiles for use in clothing is based on several commercially important properties. Improving one or two of the properties, at the expense of others, does not fulfill a perceived need for silk textiles that are comfortable and elegant, as well as machine-washable. Among the properties which consumers have come to expect in silk, are ease in handling, dimensional stability under both wet and dry conditions, resistance to slipping, elasticity, soft flowing drape, freedom from water spots, resistance from ultraviolet light, and flame retardancy.
A need currently exists for a formaldehyde-free silk finishing process which can improve the crease-resistance of silk textiles without significantly decreasing the strength or the tear resistance of the textiles. A silk finishing process which provides both crease-resistance and durability is desired.